Field of the Invention
The present disclosure relates to a toner for use in an electrophotographic system, an electrostatic recording system, and an electrostatic printing system, a two-component developer, and a method for manufacturing a toner.
Description of the Related Art
In recent years, with a rapid spread of an electrophotographic full color image forming apparatus, the uses thereof also has variously spread and a demand for image quality has also more increased more than before.
Nowadays, advances in the printing field of the electrophotographic full color image forming apparatus have been significant. Images output by the electrophotographic system have also been required to have image quality (high brilliance, high definition, granularity, and the like) equal to or higher than the image quality of images output by former printing methods.
Furthermore, there is a need for an improvement of image output speed, a reduction in running cost, stability of image quality irrespective of environments, and the like. There is a need for a toner satisfying these various needs.
The image output speed of an image forming apparatus is directly linked to productivity in the commercial printing use and relates to the operation efficiency in the use in offices. Therefore, a need for an image forming apparatus with a high image output speed (high-speed machine) has increased.
In the high-speed machine, a two-component developer containing a toner and a magnetic carrier in combination is suitably used due to high toner supply ability to a photoconductive drum. In the case of the two-component developer, strong stress is applied to a toner from the magnetic carrier as compared with a one-component developer. Therefore, there is a need for a toner having high resistance to stress.
Moreover, there is a need for a toner to have durability with which high quality images can be stably obtained even when images are continuously output for a long time period and environmental stability with which stable images can be obtained also under various temperature and humidity environments.
Heretofore, in an electrophotographic toner, an inorganic fine particle and the like has been generally externally-added to the surface of a toner particle for the purpose of adjusting the fluidity, the adhesion, the chargeability, and the like of the toner to obtain good developability, transferability, and cleaning performance.
However, when stress is applied to the toner, the inorganic fine particle is sometimes separated from the surface of the toner particle. Then, when the separated inorganic fine particle contaminates a roller-shaped charging member (hereinafter also referred to as a “charging roller”), uneven resistance arises in the charging roller to cause image defects of uneven image density in some cases.
Moreover, the fluidity of the toner decreases under the influence of the separation of the inorganic fine particle from the toner particle, and thus the charge amount distribution of the toner spreads, so that the developability of the toner is impaired, which causes the adhesion of the toner to a non-image portion, i.e., so-called fogging, in some cases.
In the case of the two-component developer, stress is applied to the toner from the magnetic carrier due to stirring in a development device. Therefore, there is a tendency that the inorganic fine particle is likely to be separated from the surface of the toner particle. In particular, when images are continuously output with a high-speed machine for a long time period, image defects caused by contaminating a charge imparting member are likely to be obvious.
Then, in recent years, an examination of externally adding various silica particles to the surface of the toner particle has been performed as one of the techniques of increasing the charge stability and the anticontamination of the charge imparting member.
Japanese Patent Laid-Open No. 2012-163623 discloses a technique of preventing the fogging to a non-image portion by adding silica particle having a specific surface area of 10.0 m2/g or more and 50.0 m2/g or less to toner particle, and then subjecting the toner particle to surface treatment by heat.
Moreover, Japanese Patent Laid-Open Nos. 2013-190646 and 2014-77930 disclose techniques of adding non-spherical silica particle to toner particle to increase the transferability and prevent image defects.
However, in the case where images are output at a high speed or in the case where images are output over a long time period, strong stress is applied to a toner from a magnetic carrier due to stirring in a development device. Therefore, there has been room for improvement to the problem of the reduction in charge stability of the toner due to the influence of humidity, the contamination of a charge imparting member, and the like.